Absolute value bars in dot product derivation

[ChiralSuperfields]

Dose someone please know why they have the absolute value bars in this derivation?

many thanks!

 

[jedishrfu]

The absolute value bars indicate the length of the vector not absolute value of a number.

Of course, the vector length is always positive.

I think this convention was more popular in early vector math books where as now they use the double v-bar notation.

https://en.wikipedia.org/wiki/Norm_(mathematics)

 

[ChiralSuperfields]

The absolute value bars indicate the length of the vector not absolute value of a number.

Of course, the vector length is always positive.

I think this convention was more popular in early vector math books where as now they use the double v-bar notation.

https://en.wikipedia.org/wiki/Norm_(mathematics)

Thank you for your help @jedishrfu !